Atheroembolism to the kidney is a well-established but poorly recognized phenomenon that tends to occur in patients with severe atherosclerosis affecting the aorta and renal arteries. This phenomenon occurs when plaques emitting cholesterol particles shower them into the renal parenchyma, mechanically blocking intra renal vessels, at the arcuate and interlobar level. In addition, these crystals induce a local foreign body response, and interlobar level. In addition, these crystals induce a local foreign body response, and interlobar level. In addition, these crystals induce a local foreign body response, leading to progressive fibrosis of the vessel, and further reducing its lumen. Plaque dissemination could be provoked by mechanical trauma during angiography, angioplasty or vascular surgery, having more acute consequences. This was well established in post-mortem and laboratory analyses. Thurlbeck and Castleman demonstrated an incidence of renal atheroembolism in > 20% in severely atherosclerotic aortic disease, with the incidence spiraling to > 70% following AAA surgery. Flory demonstrated that the emboli were cholesterol crystals occluding vessels between 55-900 microns. Kimura et al experimentally showed that the effects of embolism were dose dependent; larger showers of cholesterol emboli are more susceptible to cause renal shutdown.

It is well known that angioplasty procedures are likely to produce distal embolism. Rapp et al, in an ex vivo study of carotid angioplasty, showed that initial passage of guide wire produced emboli, but there was a significant increase during angioplasty and even more so during stent placement. Microemboli were also detected in vivo with transcranial Doppler during carotid angioplasty, having a definite spatial relationship between Doppler recognition of emboli and neurological sequelae.

There are, however, no data on renal artery Doppler recognition of emboli during intervention. Al-Hamili et al reported remarkable findings in patients undergoing iliac angioplasty. These authors recorded Doppler signals during renal angioplasty. Interestingly, signals (although low) were recorded in the femoral arteries for 2h after renal angioplasty. Imagine what the Doppler signals in the renal arteries would have reflected during renal revascularisation.

Devices were evolved to protect the distal circulation from the derogatory effects of emboli during angioplasty. They were initially used in the treatment of patients with coronary bypass graft disease; these interventions were commonly plagued by the angiographic “no reflow” phenomenon, producing clinical myocardial infarction. Use of protection devices produced significant reduction in mortality, myocardial infarction and need of emergency CABG in such patients. Similarly, better outcome was noted during carotid angioplasty when filters were used. Not surprisingly, debris was detected in 91% of coronary filters and in 84% of carotid filters following revascularisation.

The results of coronary and carotid angioplasty can be easily extrapolated in predicting outcome of renal interventions, as the atheromatous pathology and patient population are similar. Atheroembolism has long been viewed as a major risk or complication of percutaneous intervention of the renal arteries. Most studies of endovascular revascularisation in ischaemic nephropathy have reported procedure-related acute decline in renal function of 10-20% patients, largely related to cholesterol embolisation. It is important to recognize that the large functional reserve would not allow SCr to get elevated until as much as 50% of total glomerular filtration is lost. Large volume of debris would then be required to create any significant functional alteration of the kidney. However, once the SCr becomes abnormal, the curve relating GFR to SCr becomes abnormal. Small amount of renal debris can then have a dramatic outcome in deteriorating the renal function. Which makes it imperative to protect the kidney from any amount of debris blocking its arteries.

The ideal device should have the property to capture all debris, regardless of size. It should allow continued renal perfusion during the procedure, have limitless reservoir and have good technical qualities such as low profile with least vascular trauma, good trackability, easy to use and recapture. Compared with other devices, the renal device should have particular qualities; the filter length should be short for adequate renal protection. Also, the wire should be stronger to allow stent trackability at severe angulations of the renal artery take-off. Currently, there are two types of devices that could be used in renal interventions: filter devices and occlusion devices, both of which have its advantages and drawbacks.

The experience with distal protection in renal interventions has been early, with only two publications to date. Michel Henry et al had studied 28 patients (32 renal arteries) using an occlusion device. All patients had none or mild renal dysfunction. He noted visible debris in all cases, while no patient showed worsening of renal function in the 6m follow up. Another study by Holden and Hill involved the use of a filter device in 37 patients (46 arteries), all of which had some degree of pre-existing renal impairment. In this patient group, 65% of the devices contained significant debris. All patients having mild or moderate renal impairment had improvement or stabilization of renal function, whilst 5% of the patients (from the severe renal impairment group), had unchanged decline in renal function. When compared with results from the same institute without use of protection, there is a substantial benefit of usage of these devices. Our experience at Bombay Hospital is with 11 arteries in 8 patients using occlusion and filter devices. All showed stabilization/improvement in SCr levels with a mean follow up of 6 months.

While these studies are case-controlled, it would be essential to really understand the value of these devices in a randomized trial. At present there is an ongoing trial (Resist trial), the results of which are awaited. Until then, we would believe that distal protection should be offered in all patients with renal impairment, especially in those with a solitary functioning kidney, severe atherosclerosis, or when bilateral renal angioplasty is being considered.